P1121: POSITRON EMISSION TOMOGRAPHY FOR FINAL RESPONSE ASSESSMENT TO RITUXIMAB-DOSE ADJUSTED EPOCH IN PRIMARY MEDIASTINAL LARGE B-CELL LYMPHOMA: WHO IS WORTHY TO BE IRRADIATED?
Authors: Theodoros Vassilakopoulos, Alexia Piperidou, Zois Melios, Evgenia Verigou, Eirini Katodritou, Christina Kalpadakis, Sotirios Papageorgiou, Chrysovalantou Chatzidimitriou, Vassilios Prassopoulos, Marina Siakantaris, Hara Giatra, Dimitrios Kalkanis, Nikolaos Papathanasiou, Loukia Ligdi, Anastasia Kopsaftopoulou, Theoni Leonidopoulou, Vasileios Xanthopoulos, Stamatios Karakatsanis, Effimia Vrakidou, Sophia Chatziioannou, Dimitrios Drougkas, Eleftheria Hatzimichael, Gabriella Gainaru, Maria Palassopoulou, Maria Tsirogianni, Maria Kotsopoulou, Evangelia Skoura, Catherine Mainta, Evangelos Terpos, Christos Poziopoulos, Panayiotis Zikos, Argyro Koumarianou, Dimitra Liapi, Evgenia Verrou, Panayiotis Tsirigotis, Athanasios Liaskas, Maria Aikaterini Lefaki, Theodora Triantafylloy, Angeliki Georgopoulou, Vassiliki Labropoulou, Helen Papadaki, Ioannis Datseris, Argyris Symeonidis, Maria Bouzani, Themis Karmiris, Maria Bakiri, Maria Angelopoulou, Phivi Rontogianni
Journal: HemaSphere (2023)

Topic: 19. Aggressive Non-Hodgkin lymphoma - Clinical Background: ΕοΤ-PET is a valuable tool in the assessment of residual masses after first line treatment in PMLBCL and has been extensively evaluated after R-CHOP or R-MACOP-B. However, after R-da-EPOCH, the clinical significance of EoT-PET may not be the same, since most patients with positive scans achieve long-term disease control without radiotherapy (RT). The omission of RT in pts with Deauville 5-point scale score (D5PSS) 4 often causes anxiety to the treating physicians, while handling of patients with D5PSS-5 remains controversial [RT vs high dose chemotherapy and autologous stem cell transplantation (ASCT)]. Real-world data is required to shed light on the above issues. Aims: To provide an extensive real-world experience on EoT-PET imaging for response evaluation after R-da-EPOCH in PMLBCL in order to assess its clinical and prognostic significance and its effect on further treatment guidance. Methods: Among 145 pts with PMLBCL treated with R-da-EPOCH in 20 Hellenic Centers, 139 were evaluated with EoT-PET and 2 did not undergo EoT-PET but were considered as D5PSS-5, since they had progressive disease (PD) at the assumed time of EoT assessment. Cases with D5PSS-4 were retrospectively evaluated by a single nuclear medicine physician and scored visually according to the D5PSS. Freedom from Progression (FFP) was measured from the time of EoT-PET. Results: Among 141 (139 + 2) EoT-PET evaluable pts, 24 had D5PSS-1 (17%), 35 D5PSS-2 (25%), 42 D5PSS-3 (30%), 22 D5PSS-4 (16%) and 17 D5PSS-5 (12%) D5PSS-5; including the2 patients with frankly PD who did not undergo EoT-PET. A single patient (0.7%) had D5PSS-X (indeterminate) and was classified as negative. The 5-year FFP for pts with D5PSS-1,2,3,4, and 5 were 95.7%, 97.1%, 97.5%, 86.4% and 29.4% (p<0.001). D5PSS-1-3: Only 3/102 pts (3%) received RT and only 3/102 relapsed. Two relapses were associated with CNS involvement (unpreventable by mediastinal RT). One pt developed Hodgkin lymphoma and 3 t-AML. D5PSS-4: EoT-PET was available for central review in 20/22 pts. By visual interpretation, 7/20 (35%) were reclassified as D5PSS-3. Only 5/22 received RT and only 3/22 relapsed (5-year FFP 86.4%). The 5-year FFP for irradiated versus non-irradiated pts was 100% versus 82.4% (p=0.33). Following central review, 2/3 relapses were observed in pts with D5PSS-4 per central interpretation, while the last one was observed in a pt reclassified as D5PSS-3. FFP rates remained virtually unchanged. Only 3/15 revised D5PSS-4 pts had residual SUVmax>5; 2/3 did not receive RT and both relapsed compared to 0/12 of pts with SUVmax≤5. D5PSS-5: Among these 17 pts, 6 had responsive disease by conventional imaging staging and 11 had SD/PD: 5/6 with “responsive D5PSS-5” received RT and all converted to PET-negative and remain in continuous CR for a median of 26 months (range 23-44). All the 11 patients with SD/PD (“resistant D5PSS-5”) were directly forwarded to salvage chemotherapy with the intention of ASCT. The 5-year OS was 83.3% vs 40.9% for patients with “responsive D5PSS-5” or “resistant D5PSS-5” (p=0.13). Summary/Conclusion: In this large real-life study of R-da-EPOCH, RT was safely omitted in the vast majority of D5PSS 1-4 pts with PMLBCL. The reproducibility of D5PSS-4 was moderate. RT was extremely successful, and can be restricted only to the small minority of patients with “responding D5PSS-5”and “high uptake” D5PSS-4 (for example SUVmax>5), who roughly correspond to just 6% of patients who achieve a conventional response by CTs with R-da-EPOCH. A proposed algorithm is provided in the figure.Keywords: Non-Hodgkin’s lymphoma, B cell lymphoma, Lymphoma therapy, Radiotherapy